Lymphoid cells possess cell surface glycoconjugates which can be used as differentiation markers and also serve as receptors for mitogenic lectins. It has recently been shown that lymphoid cells also bear surface receptors for carbohydrates (endogenous lectins) similar to those found in a number of cell types from other species. These endogenous lectins are excellent candidates for active participation in cell-cell recognition, homing, intercellular signaling, and may also serve as a new set of differentiation markers. Our studies have shown that specific endogenous lectins do exist on subpopulations of both human and murine lymphoid cells. For example, human monocytes and a subset of suppressor T cells, both bear receptors for PWCH, an arabinoxyloglucan. These potent suppressor cells can be prepared by reversible agglutination with PWCH. In our present studies, we have synthesized fluorescent derivatives of PWCH for use in flow microfluorometry studies. We have also found that one of our synthetic glycoprotein probes appears to promote differentiation and immunoglobulin secretion by human B cells.